Polyoxyalkylene block copolymers have been used as non ionic surface active agents for many years. In general they have both hydrophobic and hydrophilic blocks which in combination give these compounds their surfactant properties. These products have been described before in numerous references. For example, Lunsted was the first to describe them in U.S. Pat. No. 2,674,619. Heterization of both the hydrophobic and hydrophilic blocks of nonionic block copolymer surfactants is well known in the art of surfactant chemistry. Lunsted, et.al. in U.S. Pat. No. 3,022,335, discloses surface active polyoxyalkylene compounds having plurality of heteric polyoxypropylene-polyoxyethylene chains, more specifically a heteric oxyalkylene-oxyethylene chain or chains as a hydrophobic nucleus to which oxyethylene chains were attached as the hydrophilic block. Patton, et. al., in U.S. Pat. No. 3,101,374, discloses surface active mixtures of polyoxyalkylene compounds composed of hydrophobic oxyalkylene chains or blocks which are condensed with a plurality of heteric oxyethylene-oxyalkylene chains. Patton also discloses that the resultant products were liquefied by addition of alkylene oxide, in a large enough percentage, to the heteric hydrophilic block. Otten & Schoene in U.S. Pat. No. 5,187,191, disclose an aqueous pesticide dispersion composed of a water insoluble pesticide, a liquid polyoxyalkylene compound having a plurality of heteric polyoxypropylene polyoxyethylene chains and water.
The aqueous gel properties and uses of solid polyalkylene/polyoxyethylene block polymers are well documented. U.S. Pat. No. 3,639,574 (Schmolka) assigned to BASF discloses polyoxyethylene/polyoxypropylene block copolymers as gelling agents for hydrogen peroxide compositions. In Lutz, U.S. Pat. No. 4,011,309, dentifrice compositions are disclosed which are composed of aqueous gel formulations that incorporate polyoxyethylene-polyoxypropylene block copolymers as the main gel component. Schmolka, in U.S. Pat. No. 4,343,785, discloses an aqueous gel dentifrice comprising polyoxybutylene-polyoxyethylene block copolymers. Schmolka also discloses mouthwash compositions which utilize polyoxybutylene-polyoxypropylene block copolymers as solubilizers.
Further, U.S. Pat. No. 3,740,421 (Schmolka) assigned to BASF discloses aqueous gels prepared using a triblock copolymer of polyoxyethylene/polyoxypropylene/polyoxyethylene suitable for pharmaceutical and personal care compositions at approximately 20-25% by weight. U.S. Pat. No. 4,465,663 (Schmolka) assigned to BASF discloses polyoxybutylene/polyoxyethylene block copolymers as gelling agents for aqueous gels useful in personal care and pharmaceutical applications. Some of these compounds are sold by the BASF Corporation under the PLURONIC.RTM. tradename.
Additionally, U.S. Pat. No. 4,272,394 and U.S. Pat. No. 4,411,810 disclose the use of polyoxyalkylene block copolymers in machine dishwashing applications. U.S. Pat. No. 4,925,988 discloses a nonionic surfactant employing a specific combination of alkanol, ethylene oxide and propylene oxide useful in an automatic dishwashing application. U.S. Pat. No. 5,374,368 describes the use of liquid EO/PO/EO triblock co-polymers (PLURONIC.RTM. L 31 and L 35 surfactants) in stable hydrogen peroxide releasing dental care compositions at levels of 55-90% by weight of the dental care composition. U.S. Pat. No. 3,867,533 discloses aqueous gel compositions containing solid EO/PO/EO triblock copolymers, having a molecular weight of 6,450-20,000 useful at levels of approximately 20% by weight. Said compositions are useful in preparing cosmetic formulations. U.S. Pat. No. 5,035,880 discloses a stable dentifrice compositions containing a cetylpyridinium bactericide and EO/PO/EO solid triblock copolymers (PLURONIC.RTM. F 127 surfactant), and polyethylene glycol at levels of 15-80% by weight. U.S. Pat. No. 4,476,107 discloses a mouthwash containing EO/BO (butylene oxide)/EO triblock copolymers at levels of 0.5-5.0% by weight. U.S. Pat. No. 5,057,307 discloses oral hygiene gels containing non-ionic surfactants, coating substances; and viscosifiers. Said non-ionic surfactants are PLURONIC.RTM. F 108 and F 127 surfactants available from BASF Corporation, Mt. Olive, N.J. U.S. Pat. No. 5,256,396 discloses a topical composition comprising an EO/PO/EO solid triblock copolymer (PLURONIC.RTM. F 127 surfactant) used at a level of more than 10% to about 17% by weight. EPO-546-627A discloses mouthwash compositions comprising solid EO/PO/EO triblock copolymers such as PLURONIC.RTM. L 108, F 88 surfactants at levels of 0.5-3% by weight. U.S. Pat. No. 5,073,368 discloses mouthwashes containing solid EO/PO/EO triblock copolymers such as PLURONIC.RTM. F 87 surfactant at levels of 0.1-3% by weight. WO 93/13750 discloses an ocular cleansing composition comprising solid PLURONIC.RTM. F 87 and paste PLURONIC.RTM. P 85 EO/PO/EO triblock copolymers. PLURONIC.RTM. P 85 surfactant is 4-9% by weight of the cleansing composition, PLURONIC.RTM. F 87 surfactant is 0.5-2% by weight of the cleansing composition. U.S. Pat. No. 5,096,698 discloses a dental creme composition containing a non-ionic triblock liquid EO/PO/EO copolymer or a solid triblock EO/PO/EO copolymer at levels of 0.1-5% by weight. Said copolymers help to prevent phase separation. PLURONIC.RTM. F 108 surfactant (solid) is most preferred, followed by PLURONIC.RTM. F 87, PLURONIC.RTM. F 127, and PLURONIC.RTM. L 72 surfactants. U.S. Pat. No. 4,272,394 discloses novel, low-foaming nonionic surfactant for machine dishwashing compositions. U.S. Pat. No. 4,411,810 discloses a low foaming, low cloud point, nonionic surfactant for machine dishwashing compositions. Finally, JP 47-48366 B4 discloses a process for producing tasteless, liquid, heteric polyoxyalkylene compounds of molecular weight 1000 or higher. U.S. Pat. No. 5,187,191 discloses polyoxyalkylene block copolymers in agricultural formulations. U.S. Pat. No. 5,496,542, U.S. Pat. No. 5,374,368, and U.S. Pat. No. 5,424,060 disclose the use of a polyoxyalkylene compound for formulating a stable percarbonate formulation as well as a dentifrice composition.
Clearly, it is known to those ordinarily skilled in the art that solid block copolymers of ethylene oxide and propylene oxide are useful in aqueous dentifrice compositions. However, a typical disadvantage with the solid block copolymers is their physical form. Triblock copolymers of ethylene oxide and propylene oxide, wherein the ethylene oxide content in the copolymer is over 70%, are typically solids above a MW of 3000. Solid, triblock copolymers of ethylene oxide and propylene oxide can pose handling problems during the manufacture of aqueous dentifrice compositions. Such difficulties typically arise due to their high melting points. In many cases, the solid triblock copolymers have to be converted to their molten state during processing.
The Applicants have surprisingly discovered that when the solid triblock copolymers are rendered liquid via a carefully controlled addition of a heteric mixture of ethylene oxide and propylene oxide to the hydrophobic propyleneoxide block, the resulting product essentially retains the properties of the solid block copolymer and has the benefit of ease of handling in formulating personal care formulations. Specifically, the Applicants' invention overcomes the problems in the art by preparing a liquid copolymer useful in aqueous oral care compositions while essentially retaining the properties of the solid block copolymer. Thus the liquid copolymer of the invention affords ready solubility in aqueous oral care compositions, increased ease of handling and pumping, and utility as gelling or solubilizing agents for such compositions.
Additionally, the references listed hereinabove describe methods of preparation for many different polyoxyalkylene polyether surfactants. However, an undesirably broad distribution of molecular weights is obtained both in the hydrophobe and hydrophile portion of the polymer. The broad distribution of molecular weight products, which result from the anionic living polymerization, may be narrowed to some extent by reduction of a side reaction which develops during propylene oxide additions. Some of the side reactions may result in terminal unsaturation. Cuscurida in U.S. Pat. No. 3,393,243, discloses a method for preparation of propylene oxide based polyether polyols with reduced content of terminal unsaturation by using CsOH as a catalyst. Ott in U.S. Pat. No. 4,764,567, discloses a method of preparation for narrow molecular weight distribution products by using CsOH during the ethylene oxide addition. Finally, Otten in U.S. Pat. No. 4,902,834, discloses an improved process for the preparation of capped polyoxyalkylene block polyethers using CsOH.
Further, the Applicants have also discovered that the use of cesium hydroxide as a catalyst in the synthesis of the liquid polyoxyalkylene block copolymers of the present invention resulted in further improvement in the gel characteristics of the liquid polymer relative to a potassium hydroxide catalyzed material.